The differentiation of pericytes and fibroblasts to fibrogenic myofibroblasts is a common response to injury in many tissues, including the pancreas, lung, kidney, and liver. However, the persistence of myofibroblasts leads to excessive extracellular matrix (ECM) deposition and contraction, resulting in fibrosis and loss of organ function. Liver fibrosis is a serious health problem occurring in response to chronic insults, including hepatitis and excessive alcohol consumption. Hepatic stellate cells (HSCs) comprise ~ 15% of total resident liver cells and are also the primary source of hepatic myofibroblasts during fibrosis. With over 1.7 million deaths attributed to liver disease annually, extensive research is underway to better understand fibrosis progression and HSC myofibroblastic differentiation. Notably, there is growing appreciation for the role of local mechanical properties in regulating HSC activation, which is the focus of the proposed project. I propose that improved understanding of the microenvironmental cues that regulate HSC differentiation is critical to the development of therapies to combat liver fibrosis, and that biomaterials with controlled biophysical properties can be used as model systems to better probe the role of local mechanics on HSC behavior. Although initial studies in the Burdick and Wells laboratories have illustrated the influence of static material mechanics on HSC differentiation, there is still a gret need for dynamic material systems to mimic the evolving properties of native tissues. Therefore, the general objective of this proposal is to develop mechanically dynamic material systems based on hyaluronic acid (HA) to model HSC phenotypic changes during the progression and regression of fibrosis. The Burdick lab has a wealth of experience in developing tunable HA biomaterials and the Wells lab has expertise in liver mechanobiology and rodent models of liver fibrosis; thus, I am ideally suited to undertake the work proposed here. In Aim 1 I will develop hydrogels that stiffen over time to model the progression of fibrosis using secondary radical crosslinking that introduces additional crosslinks into an already formed hydrogel. I hypothesize that the rate of stiffening will determine the ultimate degree of myofibroblast differentiation and fibrogenesis, with more gradual stiffening leading to intermediate phenotypes. In Aim 2 I will develop hydrogels that soften over time via hydrolysis of crosslinks to model regression of fibrosis. I hypothesize that softening materials will yield HSCs with an intermediate phenotype similar to that observed in vivo during fibrosis regression and that the rate of softening will determine the ultimate phenotype. Together, the dynamic substrates developed here will be useful as streamlined models of other disease states in the wound healing-fibrosis-cancer triad and as ex vivo tools to identify potential targets for therapeutic intervention. Together, the proposed research and training plans in addition to the strong collaborative environment at the University of Pennsylvania will guide my development as a scientist and help me meet my career goal of becoming an independent faculty member.